Lecture 5.0 Properties of Semiconductors. Importance to Silicon Chips Size of devices –Doping...
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Transcript of Lecture 5.0 Properties of Semiconductors. Importance to Silicon Chips Size of devices –Doping...
Importance to Silicon ChipsImportance to Silicon Chips
Size of devices– Doping thickness/size– Depletion Zone Size– Electron Tunneling dimension
Chip Cooling- Device Density– Heat Capacity– Thermal Conductivity
Band theory of SemiconductorsBand theory of Semiconductors
Forbidden Zone – ENERGY GAP
ValenceBand
ConductionBand
Fermi-Dirac Probability Fermi-Dirac Probability Distribution for electron energy, EDistribution for electron energy, E
Probability, F(E)=
(e{[E-Ef]/k
BT}+1)-1
–Ef is the
Fermi Energy
Difference between Difference between Semiconductors and InsulatorsSemiconductors and Insulators
Material Eg(eV)
InSb 0.18
InAs 0.36
Ge 0.67
Si 1.12
GaAs 1.43
SiC 2.3
ZnS 3.6
NiO 4.2
Al2O3 8
kBT =0.0257 eV
at 298˚K
Probability of electrons in Probability of electrons in Conduction BandConduction Band
Lowest Energy in CBE-Ef Eg/2
Probability in CBF(E)= (exp{[E-Ef]/kBT} +1)-1 )
= (exp{Eg/2kBT} +1)-1
exp{-Eg/2kBT} for Eg>1 eV @ 298K
kBT =0.0257 eV
at 298˚K
Intrinsic Conductivity of Intrinsic Conductivity of SemiconductorSemiconductorCharge Carriers – Electrons– Holes
= ne e e + nh e h
# electrons = # holes ne e (e+ h)
– ne C exp{-Eg/2kBT} ne=2(2 m*e kBT/h2)3/2 exp(-Eg /(2kBT))Ef=Eg/2+3/4kBT ln(m*h/m*e)
Semiconductor Photoelectric EffectSemiconductor Photoelectric EffectLight Absorption/Light Emission
(photodetector)/(photo diode laser)
Absorption max =hc/Eg
Photodiode LaserPhotodiode Laser
Color depends on band gap, Eg
=hc/Eg
Pb 0.37 0.27 0.33 IR detectors
Eg>3.0 transparent
Extrinsic Conductivity of SemiconductorExtrinsic Conductivity of Semiconductor
Donor Doping Acceptor Dopingn-type p-type
p= 2(2 m*h kBT/h2)3/2 exp(-Ef/kBT)
Law of Mass Action, Nipi=ndpd or =nndn
N=nd+ni
Extrinsic Conductivity of SemiconductorExtrinsic Conductivity of Semiconductor
Donor Doping Acceptor Doping
Electron DensityElectron Density
Dopant Concentration effects Electron
DensityElectrical
Conductivity
ConductivityConductivity
Intrinsic Range– Exponential with T
Extrinsic Range– Promoted to CB
– Decreasing , – Joins Intrinsic
Majority/minority Carriers
= ne e e + nh e h
Majority/minority CarriersMajority/minority Carriers
Conductivity= ne e e + nh e h
n-type ne>>nh Low number of holes due to
recombination.Law of Mass Action
– Nipi=ndpd – (For p-type Nipi =nndn )
Extrinsic Conductivity of SemiconductorExtrinsic Conductivity of Semiconductor
Donor Doping Acceptor Dopingn-type p-type
Ed = -m*e e4/(8 (o)2 h2)Ef=Eg-Ed/2 Ef=Eg+Ea/2
Wafer SalesWafer Sales
Following PRIME GRADE Si wafers are all single-side polish $14.50 each for 25 wafers each $11.00 for 50 or more (we can double side polish)– 4" P<111> 3.0-6.6 ohm-cm– 4" N<100> 4.0-6.0 ohm-cm– 4" P<111> 7.0-21.6 ohm-cm– 4" P<100> 12.0-16.0 ohm-cm– 4" P<111> 3.0-5.0 ohm-cm
http://www.collegewafer.com/